Method of producing sheet metal blanks having a varing thickness

ABSTRACT

A method of producing a flat sheet metal blank which varies in thickness. The sheet metal blank is produced for manufacturing components for motor vehicles. The method comprises the steps of providing a flat sheet metal blank having a variable thickness and prefabricated as a starting workpiece, and reworking the prefabricated flat sheet metal blank such that the variable thickness of the prefabricated flat sheet metal blank is locally changed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to German Patent Application No. 10 2008 020 473.0, filed on Apr. 23, 2008, the content of which is incorporated herein by reference.

BACKGROUND AND SUMMARY

The present disclosure relates to a method of producing flat sheet metal blanks having a varying thickness. The method relates particularly to manufacturing components for motor vehicles.

The topic of “saving weight” is becoming increasingly significant in the automotive industry and is an important goal of further development. One possibility of achieving this goal includes the use of weight- and strength-optimized sheet metal blanks for manufacturing components for the vehicle that are produced by metal forming.

For manufacturing sheet metal blanks, it is known from German Patent Document DE 199 62 754 A1 to flexibly roll metal strips so that areas of a different thickness are created over the length of the metal strip (i.e., tailor-rolled blanks—TRB).

According to the teaching of German Patent Document DE 102 46 164 A1, the sheet metal blanks produced by a TRB method are then further formed into the final shape of the structural components in a hot-forming process in the direction of the length. The blanks are hardened by means of the last forming operation in the tool.

In addition to their numerous advantages, the blanks produced in this manner also have disadvantages. Thus, strips can be rolled only on their full width in the longitudinal direction for forming sections with different thicknesses. In this case, the sudden rises in thickness always extend at a right angle to the rolling direction. Among others, this has the disadvantage that blanks of a very different width can usually not be nested in the strip in a material-saving manner as a result of the above-described type of gradations of the thickness. As a result, the demand for the starting material which, because of the rolling operation, is already very expensive, often increases to such an extent that the use of this process will no longer be economical.

It is also known to weld metal bands, which again have a varying thickness only along the area of the length of tailor-welded blanks, from several metal sheets.

In addition, there are also suggestions to optimize the thickness of blanks in special cases by metal-cutting processes in different directions.

Thus, in many cases, components should not be reinforced over the entire width for weight- and joining-related reasons. So far, it has only been possible to solve this problem by patchwork, special tailor-welded blanks or milled blanks. All these solutions are very costly and have the technical disadvantages as noted in the next few paragraphs.

In the case of patchwork, the blank and the patch have to be cut separately. They have to be formed jointly and subsequently also often still have to be welded to one another. In addition, the patches are not connected with the basic material over the whole surface. For this reason, very high expenditures are required for avoiding the crevice corrosion between the two metal sheets disposed on one another. This may even have the result that the metal sheets are first welded, or tacked, to one another, are then jointly formed, are separated again, are provided with corrosion protection and are subsequently finally welded to one another. The patchwork never reaches the strength of a massive construction consisting of one piece.

Mainly in cases in which large areas have to be cut, milled blanks are not economical because of the considerable loss of material and the high costs of the machining.

A large-surface stamping-together of blanks for achieving the thickness gradation is hardly possible even in the hot condition because of the forces and difficult forming conditions required for this purpose.

German Patent Document DE 101 45 241 C2 suggests the producing of a blank by cutting by means of a geometrically defined blade, particularly by milling, and subsequently subjecting the blank to a cold or hot forming.

In contrast, the present disclosure relates to a simplified method of producing essentially plane sheet metal blanks which each vary in their thickness at least in sections in two dimensional directions.

The present disclosure thus relates to a method of producing sheet metal blanks which vary in their thickness, the flat sheet metal blanks being produced, for example, for manufacturing components for motor vehicles. The sheet metal blank has a variable thickness and is prefabricated as a starting workpiece. The prefabricated sheet metal blank is then partially reworked, for example, by being restamped, such that the variable thickness of the prefabricated sheet metal blank is locally, or selectively, changed.

As a result of the above-described method, according to the present disclosure, it becomes possible to produce thickness-optimized sheet metal blanks in a cost-effective and high-quality manner.

The prefabricated sheet metal blank having a thickness that is variable only in a first direction is preferably taken out of a metal strip which was produced by a method for flexibly rolling, i.e., tailor-rolled blanks. In such a case, the thickness, as a rule, varies only in the rolling direction.

However, it is also within the scope of the present disclosure, that the prefabricated sheet metal blank having the variable thickness is taken from a metal strip that was soldered or welded from several metal sheets, i.e., tailor-welded blanks.

The sheet metal blank produced by the tailor-rolled blank method or the tailor-welded blank method, may be taken, or cut, from a strip and reworked only locally. This minimizes the loss of material for the reworking,such as when a cutting process is used. The cutting reworking, as well as the restamping, can additionally be carried out in a rapid and cost-effective manner.

The transitions between the areas having a different thickness can be optimized in a circumferential manner. That is, it can be further developed to be particularly soft and optimized with respect to strength.

When manufacturing thickness-optimized sheet metal blanks for producing pressure-hardened hot-formed parts, there is the possibility of first hot-stamping, for example by a rapid impact, the sheet metal blanks heated for the pressure hardening. Because of the brief contact time with the heated stamping tool, so little heat would only be withdrawn from the workpiece that the subsequent pressure hardening could take place “from heat”.

Other aspects of the present disclosure will become apparent from the following descriptions when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are two views of a sheet metal blank, according to the present disclosure, the two views being 90° perpendicular to one another.

FIGS. 2 a and 2 b are two views of the sheet metal blank of FIG. 1 after a further machining, according to the present disclosure, the two views being 90° perpendicular to one another.

FIG. 3 is a schematic view of the sheet metal blank from FIG. 1 showing a reworking by a milling tool.

FIG. 4 is a schematic view of the sheet metal blank from FIG. 1 showing a reworking by a stamping tool.

DETAILED DESCRIPTION

FIGS. 1 a and b illustrate two views of a sheet metal blank 1 which are 90° perpendicular to one another. Sheet metal blank 1 is cut from a metal strip and has a variable thickness along its length.

Metal strips of this type can be cost-effectively produced by either a tailor-rolled blank method or a tailor-welded blank method. The metal strips may be provided in a wound condition or as a strip product for further processing. Then, the contour of FIG. 1 is cut out.

Correspondingly, the sheet metal blank 1 from FIG. 1 extends in a flat manner in the X-Y plane. The sheet metal blank 1, for example, has a variable thickness Z, such as areas 2, 3, 4 with a different thickness at first only in the X-direction. In contrast, as shown, the thickness Z of the sheet metal blank 1 is constant in the Y-direction extending perpendicular to the X-direction.

Then, the thickness Z of the prefabricated sheet metal blank 1 is changed by a partial local reworking in at least one or more areas, such as areas 5, 6. The thickness is changed such that, as a result of the reworking, the sheet metal blank 1 has a variable thickness Z not only in the longitudinal direction X of the metal strip from which it was cut but also perpendicularly thereto in the Y-direction. However, it is within the scope of the present disclosure that the method provides for especially low losses in the strip of material from which the metal blanks are cut.

The resulting sheet metal blank 1, as shown in FIG. 2, is particularly suitable for the further processing into a vehicle body part.

The partial thickness change for the production of the sheet metal blank 1, as shown in FIG. 2, may preferably take place by a cutting process and, may also take place, by a local milling. The local milling may be performed by milling tool 7, as shown in FIG. 3.

However, as an alternative, according to the present disclosure, the partial thickness change can also take place by cold or hot stamping. Such cold or hot stamping may be performed using die parts 8, 9, as shown in FIG. 4.

The reworking of the tailor-rolled or tailor-welded sheet metal blanks provided with a variable thickness in one direction milling have the advantage that the loss of material and the machining expenditures for the variation of the thickness in two mutually perpendicular directions can be kept relatively low.

In addition, the stamping can be carried out rapidly and easily.

Although the present disclosure has been described and illustrated in detail, it is to be clearly understood that this is done by way of illustration and example only and is not to be taken by way of limitation. The scope of the present disclosure is to be limited only by the terms of the appended claims. 

1. Method of producing flat sheet metal blanks (1) which vary in their thickness (Z), particularly for manufacturing components for motor vehicles, by which a) a sheet metal blank having a variable thickness (Z) is prefabricated as the starting workpiece, and b) the sheet metal blank from Step a) is then partially reworked, particularly restamped, so that the thickness of the sheet metal blank a), which already has a variable thickness, is locally changed.
 2. Method according to claim 1, characterized in that the sheet metal blank (1) from Step a) having a variable thickness is taken from a metal strip which was produced by means of a method of flexibly rolling.
 3. Method according to claim 1, characterized in that the sheet metal blank (1) from Step a) is taken from a metal strip which is soldered or welded from different metal sheets.
 4. Method according to one of the preceding claims, characterized in that the local change of thickness for producing the sheet metal blank (1) takes place by means of a local cutting reworking.
 5. Method according to claim 4, characterized in that the partial thickness change for producing the sheet metal blank (1) takes place by means of milling.
 6. Method according to one of the preceding claims 1 to 3, characterized in that the partial thickness change for producing the sheet metal blank (1) takes place by means of cold stamping.
 7. Method according to one of the preceding claims 1 to 3, characterized in that the partial thickness change for producing the sheet metal blank (1) takes place by means of hot stamping.
 8. Method according to one of the preceding claims, characterized in that the blank heated for a pressure hardening is hot-stamped by a rapid impact. 